Multi-point activation trigger system and method

ABSTRACT

A trigger assembly for a paintball gun preferably includes a trigger arranged to move between a forward and a rearward position. A position transducer is preferably arranged in communication with the trigger to detect an amount of movement of the trigger. The position transducer preferably generates a signal corresponding to the amount of movement of the trigger. A control circuit preferably receives the signal from the position transducer and initiates a firing operation of a firing device when the output signal characteristics satisfy certain predetermined parameters. In one embodiment, the control circuit initiates a firing operation when a change in the output signal is greater than a predetermined threshold value. A change in the output signal can be determined by comparing a present output signal value with a reference signal value. The reference signal value can be set when the trigger is at rest or when the trigger transitions from a forward movement to a rearward movement. In another embodiment, the control circuit can be configured to adjust a firing rate of the firing device based on the amount of trigger pull.

FIELD OF THE INVENTION

This invention relates generally to triggers for pneumatic paintball guns (“markers”) or other pneumatic guns or firing devices. More specifically, this invention relates primarily to a trigger system and method for actuating a firing sequence of an electrically-operated firing device.

BACKGROUND OF THE INVENTION

Paintball is a fast-paced game, and players must be able to fire quickly and accurately to be victorious. Although paintball was originally played with purely mechanically-operated pneumatic markers, with the introduction of electronic paintball guns, a new age in paintball technology was born. Along with electronic control came the ability to precisely control the timing of gun operations. Precise electronic timing enabled much higher firing rates than previously considered possible. The extremely light triggers made possible by the use of electronic control made it possible for users to easily reach high firing rates even in pure semi-automatic mode. The industry is constantly searching, however, for ways to improve the responsiveness of the paintball gun to trigger pulls by the operator and to provide even higher firing rates and more firing mode options to the user. Other industries employing electrically-actuated firing devices would also likely benefit from an improved trigger system for those firing devices.

SUMMARY OF THE INVENTION

Conventional triggers in electrically-actuated paintball guns may use a microswitch, optical switch, or magnetic field switch to actuate the firing sequence. Although some of these methods may provide an adjustable activation point, each typically provides only a single activation point for initiating a firing operation in the paintball gun. Accordingly, there is a need for a trigger system for an electrically-actuated firing device that provides multiple adjustable or variable activation points. The industry would also benefit from a trigger system that provides additional firing mode options such as a variable firing rate fully automatic (full-auto) firing mode.

According to one aspect of this invention, an improved trigger system can provide numerous activation points. In one preferred embodiment, a potentiometer or other position transducer is electrically connected to a control circuit (e.g., a control board) and configured to be actuated by trigger movement. In this embodiment, the position transducer preferably permits monitoring of the position and movement of the trigger, including the direction of movement of the trigger throughout its course of travel. The control board preferably receives a voltage signal from the position transducer that is proportional to the position of the trigger. The control circuit can thereby monitor the position and movement of the trigger using the output voltage of the position transducer to determine when the marker should fire. Other possible position transducers that could be used include optical sensors, photocells and emitters, inductive proximity sensors, Hall effect or other magnetic resistance sensors, and other variable voltage output devices.

In a preferred embodiment, the trigger preferably has a “home” (non-actuated) position with the trigger fully forward. At the home position, the potentiometer preferably outputs a fixed voltage (V_(out)), which can, for instance, be either a zero voltage (V_(out)) output, or full voltage (V_(full)) output. In one embodiment, for example, in the trigger's home position, the potentiometer produces no voltage output (V₀). As the trigger is pulled back, however, the potentiometer is actuated, and since there is an infinite range of voltage values between the end limits (V₀, V_(full)) of the potentiometer's voltage capabilities, as the trigger pull increases, the voltage (V_(out)) supplied to the control board increases proportional to the amount of trigger pull. As the trigger moves back forward, the voltage then decreases in direct proportion to the position of the trigger.

Accordingly, based on the voltage reading at any given point in time and the voltage change over time (generated in response to the position and movement of the trigger), the control board can determine the specific position of the trigger, as well as which direction it is moving. This information can then be used by the control board to actuate a firing operation of the paintball gun based on a preselected set of position and movement parameters.

Numerous other potential embodiments are also contemplated as being within the scope of the present invention and will be readily apparent to those of skill in the art based on the following detailed description.

BRIEF SUMMARY OF THE DRAWINGS

The foregoing and additional objects and advantages of the present invention will become more readily apparent through the following detailed description, made with reference to the accompanying drawings, in which:

FIG. 1 is a somewhat schematic perspective view of a paintball gun grip frame and trigger system according to a preferred embodiment of the present invention;

FIG. 2 is a somewhat schematic perspective view of the improved trigger system of FIG. 1 shown removed from the paintball gun grip frame;

FIG. 2A is another somewhat schematic perspective view of the improved trigger system of FIG. 2;

FIG. 3 is a graphical illustration of a signal generated by trigger movement in a trigger system constructed according to the principles of the present invention, including various processing parameters for determining when to perform a firing operation;

FIG. 4 is a flow chart illustrating a logic flow process for actuating a firing sequence using the processing parameters of FIG. 3 in a trigger system constructed according to principles of the present invention;

FIG. 5 is a graphical illustration of a signal generated by trigger movement in a trigger system constructed according to principles of the present invention, illustrating alternative processing parameters for determining when to perform a firing operation; and

FIG. 6 is a flow chart illustrating a logic flow process for actuating a firing sequence using the processing parameters of FIG. 5 in a trigger system constructed according to principles of the present invention.

DETAILED DESCRIPTION

Various preferred aspects of the present invention will now be described in detail with reference to the accompanying figures. It should be noted, however, that the following description is provided by way of example only and not of limitation, and that many other implementations and embodiments of the present invention will be readily apparent to those skilled in the art based on the disclosure herein. The scope of the invention is therefore not limited to the particular embodiments described herein.

FIGS. 1-2A provide a somewhat schematic perspective view of a paintball gun grip frame 100 having an improved trigger system 120 including a trigger-actuated potentiometer 124 and of the trigger system 120 removed from the grip frame 100, according to preferred aspects of the present invention. Referring to FIGS. 1-2A, a potentiometer 124 is preferably mounted in a grip frame 100 or other location in a paintball gun (or other launching device) in such a way as to mechanically interface with the trigger 122. The mechanical interface can, for instance, be a linkage or contact point such as an articulating paddle 126 (such as those found on micro switches) between the trigger 122 and the potentiometer 124. When pulled, movement of the trigger 122 preferably actuates the potentiometer 124, varying the voltage output of the potentiometer 124 to the control circuit (e.g., on a control board 128) in proportion to the amount and direction of trigger movement. Based on various principles of this invention, therefore, a potentiometer 124 operated by a mechanical trigger 122 can be used as a position transducer. Other types of position transducers could also be used to produce a signal that is indicative of the position of the trigger 122 at numerous positions along its course of travel.

A potentiometer is typically a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. A voltage divider (or potential divider) is generally a simple linear circuit that produces an output voltage (V_(out)) that is a fraction of its input voltage (V_(in)). The voltage output (V_(out)) can therefore have a practically infinite number of values ranging between zero (V₀) and the input voltage (V_(in)) based on the position of the contact. There are three basic types of potentiometers: Linear taper, Logarithmic, and Digital. Any of these types of potentiometers could be used in this invention, however, the Logarithmic type is the presently preferred type.

The potentiometer 124 or other position transducer can be mounted in the paintball gun in any of numerous ways. For instance, the potentiometer 124 could be soldered directly to the circuit board 128 mounted within the grip frame 100 with a mechanical contact 126 communicating with the trigger 122, as in this embodiment. Alternatively, the potentiometer 124 could be mounted directly to the grip frame 100 with leads electrically connecting it to the control board 128. In still another configuration, the potentiometer 124 could be mounted directly to the pivot point 130 of the trigger 122 with leads providing an electrical connection to the control board 128. Of course, any number of other attachments between the trigger 122 and potentiometer 124 (or other position transducer) are acceptable where trigger movement generates and supplies to the control circuit 128 a signal proportionate to the position of the trigger 128 over its course of travel.

FIG. 3 is a graphical representation of a signal generated during operation of the trigger system of FIGS. 1-2A, illustrating various operating parameters of the improved trigger system 120. FIG. 4 is a schematic flow diagram illustrating the logic for determining when to actuate a firing sequence in the improved trigger system 120. Referring now to FIGS. 1-4, according to a preferred method, as the trigger 122 is moved, the potentiometer 124 or other trigger position transducer conveys an output signal (V_(out)) to the control circuit 128 that corresponds to the position of the trigger 122. At rest, a reference voltage (V_(ref)) is preferably set equal to the at rest output voltage of the potentiometer 124.

A predetermined voltage increase threshold (V_(th)) is preferably selected as representing a sufficient length of trigger pull for activating a firing sequence of the marker. Accordingly, before the control board 128 fires the marker, it would need to receive an adequate increase in voltage from the potentiometer 124 based on movement of the trigger 122. The control circuit 128 therefore preferably detects rearward movement of the trigger 122 (corresponding to a voltage increase) and actuates the initial firing sequence based on the rearward trigger movement when the change in signal voltage (V_(out)−V_(ref)) equals or exceeds the predetermined threshold value (V_(th)). Any desired threshold level (V_(th)) could be established to ensure that the rearward trigger movement was the result of an intentional trigger pull as opposed to accidental bumping or jarring of the paintball gun or trigger 122.

For instance, if the voltage threshold (V_(th)) is 1V, then a voltage increase from 0V to 1V would result in the firing of the marker, while a voltage increase from 0V to 0.5V would not. In addition, in this embodiment, continued rearward movement of the trigger 122 would preferably not result in multiple firing sequences. For instance, with a voltage threshold (V_(th)) of 1V, although the transition from 0V to 1V would initiate a firing sequence, a continued increase from 1V to 2V would not fire the marker again, even though the increase exceeds the voltage threshold (V_(th)). Rather, a subsequent firing operation would not occur until the trigger is reset by the control board based on any predetermined reset condition. If, in that same example for instance, the reference point (V_(ref)) was first reset to 1V, then the increase from 1V to 2V would fire the marker again, although the increase from 1V to 1.5V would not because the voltage change is below the threshold value (V_(th)).

Resetting the trigger, including resetting the firing reference point (V_(ref)), is preferably achieved as the control board 128 detects a decrease in output voltage (V_(out)) following the previous firing operation. The voltage reference value (V_(ref)) can be reset, for instance, each time the trigger 122 transitions from rearward to forward movement and then back again. Once the initial firing sequence is completed, the control board 128 preferably determines whether a subsequent drop in voltage (V_(out)) has taken place. Because the decrease in output voltage (V_(out)) represents a forward trigger movement, it is preferably recognized by the control board 128 as an indication that it should reset the reference point (V_(ref)) and fire on the next trigger pull resulting in a voltage increase satisfying the threshold requirement (V_(th)).

For example, suppose the threshold voltage (V_(th)) is 1V. If a first pull of the trigger 122 results in a voltage increase from 0V to 1.5V, the control board would first fire the marker when the voltage initially reached 1V (e.g., because (V_(out)−V_(ref))≧V_(th)). If a trigger release then results in a voltage drop from 1.5V to 1V, the control board 128 would then reset the firing voltage reference point (V_(ref)) to 1V when the voltage (V_(out)) began to increase again. If a subsequent trigger pull results in a voltage increase from 1V to 2V, the control board 128 would fire the marker again when the voltage (V_(out)) reached 2V (e.g., again because (V_(out)−V_(ref))≧V_(th)).

In this manner, the potentiometer 124 allows the control board 128 to fire the marker whenever the trigger 122 is pulled back a sufficient distance from any given starting position, as long as the trigger 122 has either been pulled back from the home position or a forward movement has preceded a backward movement. The trigger 122 is thereby provided with a “floating” activation point which can be any of numerous various activation points along the course of its travel.

In an alternative embodiment, a predetermined amount of forward trigger movement can be required before resetting the trigger. A reset voltage threshold (V_(reset)) (which can, for instance, be any desired voltage decrease value) could be established to determine whether a sufficient forward movement has occurred. In this embodiment, once the initial firing sequence is completed, the control board 128 then preferably determines whether the trigger position has been either fully or partially reset by a sufficient subsequent forward movement of the trigger.

To accomplish this, the rearward trigger movement results in a peak voltage that preferably provides a reset reference voltage (V_(ref2)). A voltage decrease corresponding to a subsequent forward movement must then satisfy the predetermined threshold condition ((V_(ref2)−V_(out))≧V_(reset)) for a trigger reset to take place. If the trigger reset condition is satisfied, irrespective of whether the trigger has been fully or partially reset, the control board 128 can restart the process and actuate another firing sequence as soon as a subsequent voltage increase resulting from rearward trigger movement passes the firing voltage threshold (V_(th)).

For example, suppose the threshold voltage (V_(th)) is 1V and the reset threshold voltage (V_(reset)) is 0.25V. If a first pull of the trigger 122 results in a voltage increase from 0V to 1.5V, the control board would first fire the marker when the voltage initially reached 1V, satisfying the firing condition ((V_(out)−V_(ref))≧V_(th)). The control board 128 would set a reset reference voltage value (V_(ref2)) equal to the peak voltage (1.5V). If a trigger release then results in a voltage drop from 1.5V to 1V, the control board 128 would reset the firing voltage reference point (V_(ref)) to 1V when the voltage (V_(out)) began to increase again because the reset condition ((V_(ref2)−V_(out))≧V_(reset)) was satisfied. If a subsequent trigger pull results in a voltage increase from 1V to 2V, the control board 128 would fire the marker again when the voltage (V_(out)) reached 2V, thus satisfying the firing condition ((V_(out)−V_(ref))≧V_(th)).

A trigger system constructed according to the principles of the present invention has several advantages over conventional trigger actuation systems. Initially, while other triggers may have an electronically “variable” or what is more accurately described as an “adjustable” activation point, this method differs from those conventional systems in that it doesn't provide just a single fixed activation point at which the trigger fires the marker, but rather a substantial number of possible activation points from which the trigger could fire the marker. This virtually eliminates the possibility of “short stroking” the trigger pull (i.e., pulling the trigger an insufficient distance to activate the firing sequence) which commonly occurs during rapid sequences of fire using both fingers (referred to as “walking the trigger,” the “walking technique,” or simply “walking”). The principles of this invention therefore allow players to reach much higher and more consistent rates of fire.

FIG. 5 provides a graphical illustration of process parameters of a signal generated by a trigger-actuated position transducer (e.g., such as a potentiometer) according to yet another embodiment of the present invention. Again, according to various principles of the present invention, during operation, a signal (V_(out)) generated by the trigger-actuated potentiometer varies continuously over time based on the position and movement of the trigger. Increases in voltage preferably represent a trigger pull (rearward trigger movement), while decreases in voltage preferably represent a trigger release (forward trigger movement). Of course, if desired, the system can be configured oppositely, with releases resulting in voltage increases and trigger pulls resulting in voltage decreases.

In a conventional microswitch trigger system, the microswitch is only able to detect trigger pulls that are sufficient to actuate the microswitch. When the trigger is pulled back but the pull length is not sufficient to actuate the microswitch, this is referred to as a “pre-activation mechanical short stroke.” In addition, if the trigger is pulled back a sufficient length to activate the microswitch, but is not released a sufficient length to deactuate the microswitch before a subsequent trigger pull, the trigger system cannot detect the subsequent trigger pull. This is referred to as “post-activation short stroke.”

More specifically, in a conventional microswitch or optical trigger system, the trigger begins in a forward, non-actuated position. When the trigger is pulled, no signal is sent to the control circuit until the microswitch is closed or the activation point of the optical switch is reached. Accordingly, unless the length of the trigger pull is sufficient to actuate the microswitch or optical switch, the control circuit never knows that the trigger has been pulled and will not actuate a firing sequence of the paintball gun. In addition, even if a trigger pull is sufficient to actuate the microswitch or optical switch, if the operator does not release the trigger sufficient for the microswitch to open or for the trigger to pass the optical switch activation point (e.g., full trigger reset) before initiating the next trigger pull, then the circuit board does not know that the trigger has been released and repulled and therefore will not know to initiate a second firing sequence.

Significantly, unlike the conventional microswitch system, the trigger-generated signal according to principles of the present invention is able to convey not only a position of the trigger, but also its movement and direction. Using this information, the control board can activate a firing sequence in each instance where the trigger transitions from forward to rearward movement (or vice versa, if desired). In other words, an improved trigger system constructed according to these principles can ensure that the paintball gun is fired each time the trigger is pulled, even if the length of the trigger pull would not have been sufficient to activate a microswitch or optical switch, and even if the trigger was not sufficiently released to have reset the microswitch or optical switch.

FIG. 6 is a schematic flow chart illustrating the logic for determining when to actuate a firing sequence based on the improved trigger system 120 using the parameters described with reference to FIG. 5. Referring to FIGS. 1-2A, 5 and 6, an output voltage (V_(out)) from the potentiometer 124 or other trigger position transducer can be measured to determine when rearward movement (e.g., a trigger pull) of the trigger 122 begins. When the trigger 122 is pulled, the control circuit 128 detects the voltage increase and a firing operation is initiated. The output voltage (V_(out)) is then measured to determine when the trigger 122 is released. When the trigger 122 is released, the control circuit 128 detects the voltage decrease and starts looking for the next trigger pull. When the voltage (V_(out)) begins to increase again, the control circuit 128 knows that a subsequent trigger pull has taken place and therefore initiates another firing operation of the device. This process continues, ensuring that a firing operation takes place for each trigger pull.

Therefore, according to the features and principles of the present invention, a control board can be programmed to initiate a firing operation upon an initial rearward movement of the trigger and subsequently whenever the trigger movement transitions between a forward to a rearward movement. In this way, the starting point of a trigger pull becomes substantially irrelevant to the activation sequence and the problem of mechanical short stroking of the trigger by a user can be substantially reduced or eliminated.

As described above, however, it may be desirable in some applications to restrict which trigger pulls result in a firing operation. For instance, it may be desirable to require a trigger pull of a certain length before firing the device. In such instances, any desired predetermined threshold values can be set for determining on what conditions to actuate an initial firing sequence and subsequent firing sequences. For example, the control board can be configured to only initiate firing operations when the increase in voltage resulting from a trigger pull is greater than a predetermined threshold voltage. It may also be desirable to set conditions for determining which trigger releases result in a trigger reset. In such cases, the control board could require a trigger release resulting in a voltage drop greater than a predetermined reference value before resetting the trigger.

According to yet another embodiment incorporating principles of the present invention, a signal from the position transducer could be used to determine a firing rate for the paintball gun or other electrical firing device. For instance, a voltage output from the potentiometer or other position transducer could be used to determine how far back the trigger has been pulled. With the gun configured in a fully automatic firing mode, a firing rate of the paintball gun could be established based on how far back the trigger has been pulled. A slight trigger pull (e.g., which could be configured to correspond to a low voltage output or change) could actuate the gun with a slower firing rate. A further trigger pull (e.g., which could be configured to correspond to a higher voltage output or change) could cause the firing rate to increase to a higher firing rate. A maximum trigger pull (e.g., which could be configured to correspond to a still greater voltage output or change) could cause the firing rate to reach a maximum possible firing rate for the firing device.

Having described and illustrated the principles of the invention with respect to various preferred embodiments thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. Numerous modifications of and variations to the foregoing embodiments are possible and will be apparent to those skilled in the art. For instance, various types of position transducers could be used to provide the signal to the control board corresponding to the position and direction of travel of the trigger.

An optical sensor could be used, for instance, to provide the variable output signal. An incremental/quadrature rotary encoder is one such possible optical position transducer. Rotary encoders use a disk or section of a disk that rotates about an axis to measure angular change. This is typically achieved using a solid disk with incremental holes/gaps, or a clear disk with incremental opaque or reflective areas printed on it. Unlike the conventional use of a single optical sensor to initiate a firing operation (which simply detects the interruption of a single beam for On/Off signal functionality), the trigger system constructed according to principles of this invention would preferably use two optical sensors in order to detect changes in direction and position.

A photocell could also be used as the position transducer. In this embodiment, an emitter or reflector could be mounted on the trigger with a receiver (photocell) arranged in a fixed position in the grip frame (or vice versa). Depending on the amount of light (which could, for instance, be visible or infrared light) emitted to or reflected back to the sensor from the emitter or reflector, the sensor can determine the distance and direction of travel of the trigger by measuring the change in voltage created by the photocell.

An inductive proximity sensor could also be used. This type of sensor monitors changes within a specific electro-magnetic field being generated at a set range of parameters. These changes can be caused by metal objects (e.g., a trigger) passing through the field. The changes in the electro-magnetic field could be used to determine the position and movement of the trigger.

A method for measuring permanent magnetic fields could also be used. Hall effect or magneto-resistive sensors, for instance, provide ways of measuring changes in permanent magnetic fields. One method measures magnetic field strength (distance from sensor) and the other detects the magnetic field orientation or the rotation of the magnetic field. By mounting a permanent magnet on the trigger and a sensor in the grip frame (or vice versa), either of these methods could be used to detect the position and direction of movement of the trigger.

As is evident from the foregoing description, numerous variations and modifications are possible within the spirit and scope of the present invention. The specification therefore should not be read to limit the scope of the claims. The appended claims themselves define the scope of the presently claimed invention. 

1. A trigger assembly for a firing device, said trigger assembly comprising: a trigger; a position transducer arranged in mechanical communication with the trigger to detect an amount of trigger pull and generate an output signal that is proportional to the amount of the trigger pull; and a control circuit arranged in electrical communication with the position transducer to receive the output signal from the position transducer and configured to initiate a fring operation of the firing device based on a change in the output signal from the position transducer.
 2. A trigger assembly according to claim 1, wherein the position transducer comprises a potentiometer.
 3. A trigger assembly according to claim 1, wherein the control circuit is programmed to initiate a firing operation of the firing device when a change in the output signal from the position transducer is greater than a predetermined threshold value.
 4. A trigger assembly according to claim 3, wherein the change in output signal is determined by comparing a current output signal value with a reference signal value.
 5. A trigger assembly according to claim 4, wherein the reference signal value is set equal to an output signal value approximately when the trigger transitions between a forward movement to a rearward movement.
 6. A trigger assembly according to claim 1, wherein the control circuit is configured to initiate a firing operation during operation of the firing device each time that the trigger transitions from a static position to a predetermined amount of rearward movement and from a forward movement to the predetermined amount of rearward movement.
 7. A trigger assembly according to claim 1, wherein the position transducer is arranged on a control board containing the control circuit, and wherein a mechanical contact is arranged in communication between the position transducer and the trigger.
 8. A trigger assembly according to claim 7, wherein the position transducer is a potentiometer having an armature arranged in mechanical communication with the trigger.
 9. A trigger assembly according to claim 1, wherein the position transducer is arranged in mechanical communication with the trigger at a pivot point of the trigger to detect an amount of rotation of the trigger about the pivot point of the trigger.
 10. A trigger assembly according to claim 1, wherein the control board is configured to operate the firing device in a fully automatic mode and wherein a firing rate of the firing device is determined based on an amount of the trigger pull.
 11. A paintball gun having an improved trigger assembly, said paintball gun comprising: a grip frame comprising a trigger arranged in the grip frame and configured to move between a forward position and a rearward position; a position transducer arranged in communication with the trigger to detect an amount of movement of the trigger and configured to generate an output signal that is proportionate to the amount of movement of the trigger; and a control circuit configured to receive the output signal from the position transducer and initiate a firing operation of the paintball gun based on a change in predetermined parameters of the output signal from the position transducer.
 12. A paintball gun according to claim 11, wherein the position transducer comprises a potentiometer arranged in mechanical communication with the trigger.
 13. A paintball gun according to claim 11, wherein the control circuit is configured to initiate the firing operation when the change in the output signal is above a predetermined threshold value.
 14. A paintball gun according to claim 13, wherein the change in the output signal is determined by comparing a current output signal value with a predetermined reference signal value.
 15. A paintball gun according to claim 14, wherein the predetermined reference signal value is equal to an output signal value when the trigger is at rest or an output signal value approximately when the trigger transitions from a forward movement to a rearward movement.
 16. A method of initiating a firing sequence in a firing device, said method comprising: detecting an amount of trigger pull of a trigger in the firing device; generating a signal that is proportionate to the amount of trigger pull; and initiating a firing sequence in the firing device in response to the signal.
 17. A method according to claim 16, wherein initiating a firing sequence in response to the signal comprises determining whether a change in the signal is greater than a threshold value and initiating the firing sequence when the change is greater than the threshold value.
 18. A method according to claim 17, wherein the change in the signal is determined by comparing a current signal value with a reference signal value.
 19. A method according to claim 18, wherein the reference signal value is equal to a signal value when the trigger is at rest or when the trigger transitions from a forward movement to a rearward movement.
 20. A method according to claim 16, further comprising detecting an amount of trigger release and resetting the reference signal value only when the amount of trigger release exceeds a release threshold value. 